Muscle trainer and method for the production thereof

ABSTRACT

A muscle trainer comprising curved, elongate spring elements is disclosed. The spring elements are arranged with facing concave sides and include end areas formed at each of the ends of the spring elements. The muscle trainer includes a first joint element being formed at a first end area of each spring element and a second joint element being formed at a second end area of each spring element. The spring elements are connected at their two end areas via joints formed from the joint elements. The first joint elements are designed as brackets having a bend in the direction of the concave side of the respective spring element and in each case at least partially enclosing the second joint element of the respective other spring element. A method for producing the muscle trainer and its use as a hand trainer are disclosed.

The invention relates to a muscle trainer with two spring elements, andto a method for the production of the muscle trainer.

Various types of muscle trainers for building up muscles are known inthe prior art. For example, hand trainers are used to strengthen themuscles of the hands. The user applies a force to the hand trainer and,by means of an elastic element, the hand trainer generates an opposingforce. Conventional hand trainers use a metal spring as the elasticelement. Such hand trainers have to be provided with suitable grips,which complicates their design and production. The grips are generallymade from different materials, for example from a plastic. When such ahand trainer is actuated by the user, the grips are moved toward eachother under the applied load and, when the load is removed, they springback again to the starting position.

The utility model DE 20 2014 009 325 U1 discloses a hand trainer made ofa relatively flexurally stiff surface element and of an elastic element,wherein the elastic element has a seat for the thumb, and the flexurallystiff surface element has further finger seats. The fingers other thanthe thumb are in this way brought into a fixed position relative to thethumb. The training device thus permits targeted training of the musclesof the thumb. Further parts of the hand muscles cannot be trained.

The laid-open specification DE 10 2012 108 655 A1 describes a fitnessapparatus with elastic elements, wherein the elastic elements comprisepolyurethane. Several elastic elements can be connected to one anotherin the fitness apparatus, resulting in a suitably stiffer elasticelement. However, this connection requires a fixed union, which takes upquite a lot of space. Moreover, high levels of material stress occur atthe connection when a load is applied.

It is an object of the invention to make available a muscle trainer thathas a compact format and is easy to produce. It is a further object ofthe invention to ensure that the material stress occurring in a muscletrainer when actuated is kept as low as possible. The force needed forthe actuation and the deformation that occurs should preferably becomparable to conventional muscle trainers.

A muscle trainer is proposed comprising a first curved, elongate springelement and a second curved, elongate spring element, the two springelements being arranged with their concave sides facing each other, endareas being formed at each of the ends of the two spring elements, afirst joint element being formed at a first end area of each springelement and a second joint element being formed at a second end area ofeach spring element, and the spring elements being connected to eachother at their two end areas via joints formed from the joint elements,characterized in that the first joint elements are designed as brackets,the brackets having a bend in the direction of the concave side of therespective spring element and in each case at least partially enclosingthe second joint element of the respective other spring element.

The shape of the two spring elements can, for example, be that of asubstantially rectangular plate, wherein the rectangular plate has along side and a shorter side. The end areas are arranged at the ends ofthe long side. The rectangular plate is curved, wherein the axis ofcurvature runs parallel to the short side and perpendicular to the longside. Setting aside the curvature of the spring element, the directionparallel to the short side is regarded as the transverse direction, thedirection parallel to the long side is regarded as the longitudinaldirection, and the direction perpendicular to the surface of the plateis regarded as the vertical direction. This shape of the spring elementscan also be described as a perpendicular cylinder segment, wherein thebase surface of the perpendicular cylinder segment is substantiallycrescent-shaped. The direction parallel to the connection of the twoends of the crescent shape is designated as the longitudinal direction,and the direction perpendicular to the base surface of the cylinder isdesignated as the transverse direction. The vertical direction isperpendicular both to the longitudinal direction and also to thetransverse direction. The two end areas of a spring element are arrangedat the ends of the crescent shape as described here.

The muscle trainer comprises two such elongate, curved spring elements,which are arranged relative to each other in the muscle trainer in sucha way that their concave sides face each other. The two spring elementsare connected to each other at their ends by joints. The muscle traineris preferably composed of precisely two spring elements.

Each of the spring elements has a joint element at both of its endareas, wherein a respective first joint element of a spring elementforms a joint together with a second joint element of the respectiveother spring element. The two joints thus formed connect the two springelements in such a way that, when the muscle trainer is actuated with aforce being applied parallel to the vertical direction, the connectionsbetween the two spring elements are advantageously subjected to no oronly very slight bending loads and bending stresses. The greatestbending load is applied to the part of the spring element lying at thecenter between the two end areas. The term bending stress signifies themechanical stress in the material. The spring element is preferablydesigned in such a way that the bending stress is maintained more orless constant along the length of the spring element. The term bendingload signifies the bending moment, which decreases from the center ofthe spring element toward the edge.

When the muscle trainer is actuated, an opposing force is generated bythe spring elements, and a person using the muscle trainer has to workagainst this opposing force. The magnitude of the opposing force isdetermined by the shape of the spring elements and by the material usedand depends on the muscles that are to be exercised using the muscletrainer and/or on the training status of the user. The muscle trainer ispreferably designed as a hand trainer.

The wall thickness of a spring element preferably varies in thelongitudinal direction, i.e. along the length from one end to the otherend, wherein the greatest wall thickness is preferably reached at thecenter. The greatest wall thickness preferably lies in the range of 2 to8 mm and particularly preferably in the range of 3 to 6 mm. The smallestwall thickness preferably lies in the range of 0.5 to 5 mm andparticularly preferably in the range of 1 to 3 mm. By virtue of thevariation of the wall thickness, the spring element can be madestrongest in those areas where the greatest bending loads occur. Thefirst spring element and the second spring element preferably have thesame wall thickness or the same profile of the wall thickness.

Alternatively or in addition, the width of the spring element, i.e. thelength of the short side, can vary in the longitudinal direction. Thespring element preferably has its greatest width at the end areas.Depending on the intended use, the greatest width preferably lies in therange of 20 mm to 150 mm. In the use as a hand trainer, the greatestwidth is preferably in the range of 20 mm to 50 mm and particularlypreferably in the range of 25 mm to 35 mm. The smallest width preferablylies in the range of 5 mm to 100 mm. In the use as a hand trainer, thesmallest width preferably lies in the range of 5 mm to 35 mm andparticularly preferably in the range of 10 mm to 25 mm. If there is novariation of the width, then the width of the spring elements ispreferably chosen in the range of 20 mm to 150 mm, or, in the use as ahand trainer, preferably in the range of 20 mm to 50 mm. The firstspring element and the second spring element preferably have the samewidth or the same profile of the width.

The length of the spring elements, i.e. the extent in the longitudinaldirection, preferably lies in the range of 150 mm to 350 mm, or, in theuse as a hand trainer, particularly preferably in the range of 180 mm to230 mm.

The muscle trainer is preferably actuated in such a way that force isapplied in the area of the center of the surfaces of the springelements. For this purpose, it is preferable for a force introductionarea to be formed on each of the spring elements, such that the muscletrainer is easier for the user to use or grip. In the case where themuscle trainer is designed as a hand trainer, the force introductionareas are preferably designed as grips. The force introduction area ispreferably formed at the center of the spring elements, viewed in thelongitudinal direction of the spring elements.

The maximum spring force of the muscle trainer, providing an opposingforce upon actuation, is set through the choice of the geometry of thespring elements and through the choice of the material of the springelements and preferably lies in the range of 40 to 300 N andparticularly preferably in the range of 50 to 120 N. The maximum springforce is reached when, under the application of force, the springelements are deformed in such a way that the spring elements touch eachother in the area of the center of the surfaces of the spring elements.In this state, the curvature of the spring elements is substantiallycanceled by the deformation. The maximum possible deformation uponactuation of the muscle trainer is defined by the greatest distancebetween the two spring elements and is predetermined by the curvature ofthe spring elements. The greatest distance between the two springelements preferably lies in the range of 20 mm to 200 mm or, in the useas a hand trainer, particularly preferably in the range of 50 to 100 mm.The maximum spring force and the maximum spring deformation can also belimited (e.g. in order to achieve more comfortable operation in the useas a hand trainer) by spacers introduced between the force introductionareas of the two spring elements. In this case, the curvature of thespring elements is not completely canceled even when the maximum springforce is applied.

The two joint elements are preferably rounded, and the brackets eachform a bearing in which the respectively enclosed second joint elementis mounted rotatably. The first joint element of both spring elements isin each case designed as a bracket, wherein the bracket has a bend inthe direction of the concave side of the spring element. In the areaadjoining the spring element, the brackets have a small bend radiuscompared to the curvature of the spring element. The brackets preferablyrun out in an area that is not curved or that is only slightly curved.The area with the small bend radius forms a bearing for the other jointelement. The small bend radius is preferably adapted to the roundedshape of the second joint element. The second joint element of a springelement is mounted rotatably in the first joint element or the bracketof the other spring element such that, when the muscle trainer isactuated, the joint elements of the spring elements can execute arotational movement relative to those of the other spring element. Thismutual mobility avoids or minimizes the flexural stress in the area ofthe joints when the muscle trainer is actuated. The second jointelements are preferably designed as rollers, of which the radiuspreferably corresponds to the small bend radius of the bracket.

The spring element preferably merges tangentially into the bracket.Alternatively, it is possible for the transition from the spring elementto the bracket to be designed in such a way that the bracket curved inthe direction of the concave side of the spring element is angled in thedirection of the convex side of the spring element.

The first spring element and the second spring element preferably havean identical geometry. Two such identical spring elements in this caseform the muscle trainer, wherein the first spring element and the secondspring element are arranged relative to each other such that the concavesides of the spring elements face toward each other and, at the ends ofthe spring elements, a first joint element adjoins a second jointelement of the respective other spring element. In this way, it isadvantageous that no different parts have to be produced, and thereforethe two spring elements are able to be produced using the same tool, forexample an injection mold. The two spring elements are preferablyproduced as two separate parts. Two identical spring elements can bejoined together by turning one of the two spring elements about thetransverse axis in such a way that the brackets at least partiallyenclose the second joint elements.

Preferably, in each case a joint element of the first spring elementestablishes a form-fit connection with a joint element of the secondspring element, which form-fit connection prevents a lateral movement ofthe first spring element relative to the second spring element. Alateral movement is regarded here as a movement parallel to thetransverse direction defined for the spring elements.

The form-fit connection is preferably provided by in each case at leastone snap-in hook on the second joint element of the spring element, saidsnap-in hook engaging in each case in a corresponding opening or incorresponding recesses on the bracket or in the first end area of thejoint element of the spring element. The snap-in hook extends from thesecond joint element substantially in a direction which lies in theplane enclosed by the longitudinal direction and the vertical direction,such that relative movements of the corresponding joint elements indirections parallel to the transverse direction are prevented.

The snap-in hook preferably points in the vertical direction since, byinteraction with the opening in the first end area, it then not onlyprevents the relative movement in the transverse direction but alsoprevents a relative movement in the longitudinal direction.

The form-fit connection is additionally secured by the fact that aprojection on the snap-in hook bears on the outer face of the otherspring element. The snap-in hook is arranged and designed in such a wayas to prevent, by means of the form-fit connection, both a movement ofthe first spring element relative to the second spring element in thetransverse direction and also a movement in the longitudinal directionand in the vertical direction. Only a rotational movement about thetransverse axis of the joint is possible. For this purpose, the snap-inhook is guided through the opening, and its projection engages over theouter face of the other spring element.

Viewed in the vertical direction, the second joint element preferablyhas an opening under the snap-in hook, such that the spring element hasno undercuts in the vertical direction.

Alternatively or in addition, the wall thickness of the bracket, seenacross the width of the spring element, can vary continuously, whereinthe wall thickness is greatest, for example, at the center and decreasestoward the side edges. The wall thickness or, in the case of a secondjoint element designed as a roller, the diameter of the second jointelement of the spring element, seen across the width of the springelement, accordingly also has a variation, wherein the wall thickness orthe diameter is at its smallest at the center and increases toward theside edges. The joint elements are here regarded as part of the springelement, such that the described variation of the wall thickness cantake place at the joint elements and/or at the end areas of the springelements.

The joints of the proposed muscle trainer securely connect the twospring elements, such that an unwanted separation of the spring elementsdoes not take place. In preferred embodiments, relative movements of thepaired joint elements are suppressed in all three spatial directions,wherein a rotational movement remains possible upon actuation of themuscle trainer. By means of this rotational movement, bending stressesupon actuation of the muscle trainer are advantageously substantiallyavoided in the end areas. The joints are advantageously compact and takeup little room.

The muscle trainer is preferably composed of two pieces, wherein eachpiece comprises one of the spring elements. The first spring element andthe second spring element are preferably both free of undercuts. Thispermits simple production of the spring elements by injection molding.Advantageously, the mold does not require movable slides, such thatcost-effective production is permitted.

Printed details can preferably be provided on the muscle trainer bymeans of elevations or depressions.

The two spring elements are preferably produced from a thermoplastic.

The thermoplastic is preferably chosen from polyoxymethylene (POM),polybutylene terephthalate (PBT), polyamide (PA),acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP).

To realize good sliding characteristics, in the case of which only lowfriction and no generation of noise arise during a movement of the jointelements relative to one another, in each case different materialsshould be used for the two spring elements, in a known manner. Forexample, one of the spring elements is manufactured frompolyoxymethylene (POM) and the other spring element is manufactured froma thermoplastic material that differs therefrom. A disadvantage of thisapproach is however that the two spring elements possibly have differentcharacteristics, in particular shrinkages.

As an alternative to this, it is possible for both spring elements to bemanufactured from the same thermoplastic material, wherein atribologically modified thermoplastic material is used. In particular,tribologically modified polyoxymethylene (POM) is suitable for thispurpose. For an optimization of the tribological characteristics of thematerial, a silicon oil is normally added as an additive to the POM forthis purpose. A suitable tribologically modified POM is available underthe designation Ultraform N 2320 003 TR. In this design variant, it ispreferable for both spring elements to be manufactured from thetribologically modified POM. This has the advantage that distortion orshrinkage during the manufacturing process affects both spring elementsequally, such that the spring elements can be assembled to form themuscle trainer without problems and in an accurately fitting manner.

The plastic of the spring elements can be reinforced or non-reinforced,it being possible for a fiber-reinforced plastic to have a fiber contentof up to 60% by weight. Suitable fibers are chosen, for example, from,glass fibers, aramid fibers, carbon fibers. The fibers can be present asshort fibers, long fibers or “endless fibers”. The stiffness of thespring elements, and therefore the stiffness of the muscle trainer, canbe deliberately influenced by way of the fiber content.

Moreover, the plastic can contain further additives according torequirements.

The force introduction areas of the spring elements preferably eachcomprise a force introduction element. The force introduction elementpreferably encloses the force introduction areas of a spring element.

The force introduction element, which is preferably designed a grip inthe case of use as a hand trainer, can be made from a material otherthan the material of the spring elements. In order to achieve hapticsthat are acceptable for the user, a material is preferably used which issoft by comparison with the material of the spring elements. Forexample, the force introduction element is produced from a thermoplasticelastomer (TPE), for example a thermoplastic polyurethane (TPU). Theforce introduction element can be compact or foamed. For foamed forceintroduction elements, a polyurethane foam is preferably used.

The force introduction element preferably has a spacer on the concaveside of the spring element, which spacer limits the bending of themuscle trainer.

A further aspect of the invention concerns providing a method forproducing one of the described muscle trainers. To this end, a method isproposed comprising the steps of:

a) producing the first spring element and the second spring element byinjection molding using an injection mold,

b) arranging the first spring element and the second spring element suchthat their concave sides are directed toward each other and such that,at the ends of the spring elements, a first joint element adjoins asecond joint element of the respective other spring element,

c) bending the ends of the first spring element and of the second springelement by applying force to the spring elements,

d) snapping a second joint element into a first joint element, such thatthe first joint elements each at least partially enclose a second jointelement of the respective other spring element,

e) terminating the force application, wherein the joint elements of thespring elements form joints.

In step a) of the method, the two spring elements are produced byinjection molding. In particularly advantageous variants of the method,the two spring elements do not have any undercuts, such that the atleast one injection mold used has no slides. The injection mold cantherefore be produced particularly simply and cost-effectively.

Moreover, both spring elements are identical in terms of their geometry,such that they can be produced in the same cavity of the tool or in thesame injection mold. The identical nature of the geometry of the twospring elements also ensures that they have the same warpage after theproduction process. By means of warpage occurring after the injectionmolding, in particular during cooling, the actual geometry of the springelement produced deviates from the desired geometry. Since the firstspring element and the second spring element have an identical geometry,any warpage that occurs will influence both spring elements equally. Itis therefore easily possible for the two spring elements to be arranged,according to step b) of the method, such that a first joint element anda second joint element adjoin each other at both ends of the springelements. Spring elements that differ in geometry could warp todifferent extents, which would prevent the formation of the joints.

After the production of the two spring elements, the joints are not yetbrought together. To insert a second joint element of the springelements into the corresponding first joint element of the other springelement, the two spring elements, in step b), are accordingly arrangedrelative to each other. This can be done, for example, by turning one ofthe two spring elements about the transverse axis.

In step c) of the method, forces are exerted on the first spring elementand on the second spring element. The forces are preferably exerted atthe force introduction areas of the spring elements, wherein for exampleone of the spring elements can lie on a support and, by way of a ram,force is applied to the force introduction area of the other springelement. The two spring elements are thereby bent, and their curvaturedecreases, such that the second spring element can be inserted into thefirst spring element in accordance with step d). Thereafter, theapplication of force to the first spring element and to the secondspring element is terminated (step e)). The one or more spring elementsspring back to their respective starting position, whereupon a form-fitconnection is established and the joints are formed. The muscle traineris ready for use.

If the force introduction areas of the spring elements have forceintroduction elements, for example grips, made from a material otherthan that of the spring elements, then, in step a), after production ofthe spring elements, the latter are inserted into a further mold inorder to produce the force introduction elements or, by pulling backslides, a corresponding mold for producing the force introductionelements is generated. The force introduction elements can then beinjected onto the spring elements.

Alternatively, the force introduction elements can also be producedseparately and then connected to the spring elements by a form-fit orforce-fit engagement and/or by a cohesive fit.

A further aspect of the invention concerns the use of one of thedescribed muscle trainers as hand trainer, arm trainer or leg trainer,with a use as hand trainer being preferred.

EXAMPLES

Various muscle trainers designed as hand trainers and each havingidentical geometric dimensions were produced. The thermoplastic used forthe spring elements was varied in each case in order to produce handtrainers with different stiffness or different spring forces.Polyoxymethylene (POM) was used as the thermoplastic, the POM beingnon-reinforced in one example and being reinforced, in five otherexamples, with different contents of glass fibers.

The spring elements produced have a curved, elongate shape, wherein thewidth of the spring elements is 25 mm at the ends and 19 mm at thecenter of the spring elements. The length of the spring element withoutapplication of force, measured as direct connection line between the twoends, is 204 mm. The wall thickness of the material is 2.5 mm at theends and 5 mm at the center. The curvature of the spring elements issuch that, in the assembled state, the two spring elements are at adistance of 59 mm from each other at the center.

To calculate the opposing force of the spring elements during use in themuscle trainer, it was first necessary to determine the modulus ofelasticity of the various plastics. To measure the modulus of elasticityof the plastic, specimens were produced and, in the tensile test as perISO 527-2:1993, the force and the change in length were measured at adefined testing speed. The tensile tests were carried out on specimensmade of polyoxymethylene (POM) with different glass fiber contents; thedetermined moduli of elasticity, which describe the stiffness of thespecimen, are listed in Table 1. These were each determined at a testingspeed of 1 mm/min.

TABLE 1 Modulus of elasticity Material [MPa] at 1 mm/min POMnon-reinforced ~2700 POM with 5% by weight fiber content ~3500 POM with10% by weight fiber content ~4600 POM with 15% by weight fiber content~5950 POM with 25% by weight fiber content ~8800

The tensile tests show that, by addition of 5 to 25% by weight of glassfibers, the modulus of elasticity of the material can be increased from2700 MPa for non-reinforced material to 8800 MPa for material reinforcedwith 25% by weight glass fiber content.

The calculation revealed that spring elements with a glass fiber contentof 25% by weight were already too stiff for use as hand trainers.Therefore, spring elements for hand trainers were produced fromnon-reinforced material and from five materials with different glassfiber content. In each case, two identical spring elements wereassembled to form a hand trainer, and the stiffness of the hand trainersproduced was determined. For this purpose, a hand trainer was placed ina test apparatus in which a ram was used to exert force vertically onthe force introduction area of one of the spring elements. The otherspring element lay on a table, such that the hand trainer wasincreasingly pressed together by the exerted force. The deformationtravel of the hand trainer and the exerted force were measured.

The measurement results for the five tested hand trainers are shown inFIG. 8. In the diagram in FIG. 8, the deformation travel is plotted inmm on the X axis and the force is plotted in N on the Y axis.

From the force-travel curves in FIG. 8, it will be seen that the handtrainers present a slightly non-linear behavior in the case of a shortdeformation travel, wherein the force needed for a defined deformationis increased with an increasing fiber content in the hand trainers withspring elements made from the fiber-reinforced material. The handtrainer made from the non-reinforced material has a stronger non-linearbehavior, such that the force needed for a deformation up to adeformation of approximately 3 mm is at first approximately exactly ashigh as in the hand trainer with a 10% by weight fiber content. At adeformation travel of 10 mm, the force of the hand trainer made fromnon-reinforced material needed for the deformation corresponds to thatof the hand trainer with a 5% by weight fiber content. Above 10 mm, allthe hand trainers made from materials reinforced with fibers require agreater force than the hand trainer made from the non-reinforcedmaterial.

The stiffness of a hand trainer is defined as the gradient of theforce/travel curve. On account of the slight non-linearity, thestiffness decreases slightly as the deformation travel increases.

The stiffness for the range of 15 mm to 20 mm deformation travel wasevaluated in the range of the maximum measured deformation of 20 mm. Thestiffness determined for the tested hand trainers is shown in Table 2.

TABLE 2 Stiffness Material [N/mm] POM non-reinforced 1.2 POM with 5% byweight fiber content 1.5 POM with 10% by weight fiber content 1.7 POMwith 12.5% by weight fiber content 2.1 POM with 15% by weight fibercontent 2.4 POM with 20% by weight fiber content 2.9

Illustrative embodiments of the invention are shown in the figures andare explained in more detail in the following description.

In the figures:

FIG. 1 shows a first embodiment of a muscle trainer in a view from thefront,

FIG. 2 shows a perspective view of an attached joint of the muscletrainer,

FIG. 3 shows the muscle trainer of the first embodiment in a view fromabove,

FIG. 4A shows an attached joint in the undeformed state of the muscletrainer in a view from the front,

FIG. 4B shows an attached joint in the deformed state of the muscletrainer in a view from the front,

FIG. 5 shows a front view of a spring element of an embodiment as a handtrainer with grips,

FIG. 6 shows the hand trainer with grips in a view from below,

FIG. 7 shows a test arrangement for determining the stiffness of themuscle trainer,

FIG. 8 shows a force-travel diagram for various illustrative embodimentsof the hand trainer.

In the following description of the illustrative embodiments of theinvention, identical or similar elements are designated by identicalreference signs, and the description of said elements is not repeated inevery instance. The figures are purely schematic depictions of thesubject matter of the invention.

FIG. 1 shows a first embodiment of a muscle trainer 1 in a view from thefront. The muscle trainer 1 comprises two elongate, curved springelements 11,12, namely a first spring element 11 and a second springelement 12.

The two spring elements 11, 12 are crescent-shaped in the view from thefront, a first joint element 15 being arranged at a first end area 13and a second joint element 16 being arranged at a second end area 14.The two spring elements 11,12 are arranged relative to each other in themuscle trainer 1 in such a way that their concave sides face each other.

The direction parallel to a connection of the two end areas 13, 14 ofthe crescent shape is designated as the longitudinal direction. Thedirection extending perpendicularly with respect to the drawing plane inFIG. 1 is designated as the transverse direction. The vertical directionis perpendicular both to the longitudinal direction and also to thetransverse direction.

In the illustrative embodiment shown, the first joint element 15 of thefirst spring elements 11, 12 is designed as a bent bracket 18, whereinthe area of a bracket 18 directly adjoining the spring element 11, 12 iscurved in the same direction as the respective spring element 11,12 buthas a much smaller bend radius. In the embodiment shown in FIG. 1, thebracket does not tangentially adjoin the form of the spring element 11,12 and is instead arranged at an angle.

In the illustrative embodiment shown, the second joint element 16 of thespring elements 11, 12 is designed as a roller 24, wherein the radius ofa roller 24 corresponds substantially to the bend radius of a bracket18. The rollers 24 are oriented with their axes parallel to thetransverse direction and each adjoin an end of the spring elements 11,12. A bracket 18 forms a bearing in which a roller 24 is rotatablymounted. In further variants, instead of rollers 24 as second jointelements 16, it is possible, for example, for the second end areas 14 ofthe spring elements 11, 12 to be rounded, wherein the radius of therounding preferably corresponds to the bend radius of the bracket 18.

At the center, the spring elements 11, 12 have force introduction areas8. When the muscle trainer 1 is actuated, forces act on the forceintroduction areas 8 perpendicularly with respect to the spring elements11, 12. In this way, the spring elements 11, 12 bend elastically. Nobending stresses or only very slight bending stresses occur at the endareas 13, 14 of the spring elements 11, 12, since the joint elements 15,16 permit a rotation. The greatest bending load occurs at the center ofthe spring elements 11, 12 and decreases in the direction of the endareas 13, 14. Accordingly, it is preferable to vary the wall thicknessof the spring elements 11, 12 in accordance with the bending load,wherein the spring elements 11, 12 have their greatest wall thickness 7at the center, and the wall thickness decreases toward the end areas 13,14, such that the spring elements 11, 12 have their smallest wallthickness 6 at the end areas 13, 14. The longitudinal extent of thespring elements 11, 12 is indicated by reference sign 2 in FIG. 1 and isrelated to the unloaded state.

FIG. 2 shows a perspective view of a joint of the muscle trainer 1.

The joint of the muscle trainer 1 shown in FIG. 2 is formed from thefirst joint element 15 of the first spring element 11 and from thesecond joint element 16 of the second spring element 12.

The first joint element 15 of the first spring element 11 is a bracket18 which is curved in the same direction as the first spring element 11but which has a substantially smaller bend radius. The curvature of thebracket 18 does not tangentially adjoin the curvature of the firstspring element 11. An angle, which is less than 180°, is enclosedbetween the part of the bracket 18 bordering the spring element 11 andthe convex side of the first spring element 11.

The second joint element 16 of the second spring element 12 is roundedand, in the illustrative embodiment shown, designed as a roller 24,wherein the radius of the roller 24 corresponds substantially to thebend radius of a bracket 18. The axis 22 of the roller 24 is orientedparallel to the transverse direction. The bracket 18 forms a bearing 20,in which a roller 24 is mounted rotatably.

The second joint element 16 has, in addition to the roller 24, a snap-inhook 26, with a projection 28 arranged at the end of the snap-in hook26. The snap-in hook 26 with the projection 28 extends through anopening 30 in the bracket 18. A width 34 of the opening 30 is chosensuch that it corresponds to the width of the snap-in hook 26, with theresult that a form-fit connection is established which prevents amovement between the two spring elements 11 and 12 in the transversedirection. The length 32 of the opening 30 is substantially greater thanthe corresponding dimension of the snap-in hook 26, such that arotational movement of the second joint element 16 in the first jointelement 15 is still possible. In the unloaded state, the snap-in hook 26bears with the projection 28 on the edge of the opening 30 facing towardthe center of the first spring element 11, wherein the snap-in hook 26,by means of form-fit connection, prevents a relative movement of thespring elements 11 and 12 in the longitudinal direction. In addition tothe interaction of bracket 18 and roller 24, the projection 28 on thesnap-in hook 26 prevents a relative movement of the two spring elements11, 12 in the vertical direction. When the muscle trainer 1 is actuatedby forces being applied to the force introduction areas 8 of the springelements 11, 12, the snap-in hook 26 with the projection 28 moves to theopposite side of the opening 30, wherein a relative movement separatingthe joint elements 15, 16 is ruled out on account of the acting force.

The muscle trainer 1 of the first embodiment, described with referenceto FIGS. 1 and 2, is shown in a view from above in FIG. 3.

In this view from above, in conjunction with the view from the front inFIG. 1, it will be seen that the shape of the spring elements 11, 12 canbe described as a perpendicular cylinder segment, which has thecrescent-shaped base surface visible in FIG. 1. The view from abovelikewise shows that the snap-in hook 26 with its projection 28 of thesecond joint element 16 of the second spring element 12 is pushedthrough the opening 30 in the bracket 18 of the first spring element 11.The bracket 18 of the second spring element 12 at least partiallyencloses the second joint element 16 of the first spring element 11 (notvisible in FIG. 3; cf. FIG. 1),

In the illustrative embodiment shown in FIGS. 1 to 3, the width 5 of thespring elements 11, 12 is constant along the entire length 2 of thespring elements 11, 12.

FIG. 4A shows an attached joint in the unloaded or undeformed state ofthe muscle trainer 1 in a view from the front. In FIG. 4B, the attachedjoint is shown in the loaded or deformed state of the muscle trainer 1in a view from the front. In order to better illustrate the function ofthe attached joint, the first spring element 11 is shown partially insection in FIGS. 4A and 4B.

As has already been described with reference to FIGS. 1 and 2, the firstjoint element 15 of the first spring element 11 is designed as a bracket18, which is curved in the same direction as the first spring element11. The bend radius of the bracket is smaller than the bend radius ofthe curvature of the spring elements 11, 12 and corresponds to theradius of the second joint element 16 designed as roller 24. Thecurvature of the bracket 18 does not tangentially adjoin the curvatureof the first spring element 11. An angle, which is less than 180°, isenclosed between the convex side of the bracket 18 and the convex sideof the first spring element 11.

The second joint element 16 is designed as a roller 24 and is mountedrotatably in the bearing 20 formed by the bracket 18.

The second joint element 16 has, in addition to the roller 24, thesnap-in hook 26, with a projection 28 arranged at the end of the snap-inhook 26. The snap-in hook 26 with the projection 28 extends through anopening 30 in the bracket 18.

In the unloaded state shown in FIG. 4A, the snap-in hook 26 bears withthe projection 28 on the edge of the opening 30 facing toward the centerof the first spring element 11, wherein the snap-in hook 26, by means ofform-fit connection, prevents a relative movement of the spring elements11 and 12 in the longitudinal direction and the projection 28 prevents arelative movement of the spring elements 11 and 12 in the verticaldirection.

FIG. 4B shows the muscle trainer 1 in a loaded state brought about byactuation of the muscle trainer 1. When forces are applied to the forceintroduction areas 8 of the spring elements 11, 12, the snap-in hook 26with the projection 28 moves to the opposite side of the opening 30. Atmaximum loading, when the curvature of the spring elements 11, 12 iscanceled out, the snap-in hook 26 preferably bears on the outwardlyfacing edge of the opening 30.

FIG. 5 shows an embodiment of the spring elements 11, 12 for a muscletrainer 1 designed as a hand trainer. Since both spring elements 11, 12are identical, only one of the spring elements 11, 12 is shown in orderto provide a better view of the joint elements.

As has already been described with reference to FIG. 1, the springelements 11, 12 have, at their first end area 13, a first joint element15 designed as a bracket 18 and, at their second end area, a secondjoint element 16 designed as a roller 24. A snap-in hook 26 with aprojection 28 is additionally arranged on the roller 24.

The spring element 11, 12 of the hand trainer shown in FIG. 5 has, atthe force introduction area 8, a force introduction element in the formof a grip 36. The grip 36 encloses the spring element 11, 12 in theforce introduction area 8 thereof. The grip 36 is preferably made from amaterial other than that of the spring elements 11, 12. In order toimprove the haptics, a material is preferably chosen here which is softby comparison with the material of the spring elements 11, 12. Forexample, the grip 36 can be made from a non-foamed or a foamedpolyurethane.

In the embodiment shown in FIG. 5, the grip 36 is produced from acompact non-foamed thermoplastic polyurethane (TPU). Moreover, thespring element 11, 12 has a spacer 38 arranged on the concave side,which spacer 38, in this embodiment, is produced in one piece with thegrip 36. The maximum possible bending of a hand trainer formed from twospring elements 11, 12 is limited by the spacer 38.

The wall thickness of the spring element 11, 12 in FIG. 5 varies alongthe length of the spring element 11, 12, wherein the spring element 11,12 has its greatest wall thickness 7 at the center, and the wallthickness decreases toward the end areas 13, 14, such that the springelement 11, 12 has its smallest wall thickness 6 at the end areas 13,14. The longitudinal extent of the spring element 11, 12 is indicated byreference sign 2 in FIG. 5 and is related to the unloaded state.

FIG. 6 shows a muscle trainer 1 which is composed of two of the springelements 11, 12 shown in FIG. 5 and which is designed as a hand trainer.FIG. 6 shows the hand trainer in a view from below.

In contrast to the muscle trainer of the first embodiment shown in FIGS.1 and 3, the width of the spring element 11, 12 is not constant andinstead increases from the center to the end areas 13, 14. The springelements 11, 12 thus have their smallest width 5 and the center and havetheir greatest width 30 at their end areas 13, 14. In conjunction with avariation of the wall thickness of the spring elements 11, 12, which ispreferably greatest at the center as shown in FIG. 5, the stress in thespring elements 11, 12 is uniform along their entire length 2 in such anembodiment.

FIG. 7 shows a schematic view of a test arrangement for determining thestiffness of a muscle trainer.

To determine the stiffness, a force-travel measurement is carried out inwhich a deformation travel 48 is determined. For this purpose, themuscle trainer 1 to be tested is placed on a table 46, wherein one ofthe spring elements 12 bears with its force introduction area 8 on thetable 46. A force F is exerted on the force introduction area 8 of theother spring element 11 via a ram 44. The distance between the twospacers 38 thereby decreases from a first distance 40 to a seconddistance 42. The difference between the first distance 40 and the seconddistance 42 corresponds to the deformation travel 48.

The deformation travel 48 and the associated force F are recorded duringthe measurement.

FIG. 8 shows a force-travel diagram for various illustrative embodimentsof the hand trainer.

In the diagram in FIG. 8, the deformation travel is plotted in mm on theX axis and the force is plotted in N on the Y axis. The diagram showsmeasurements for six different examples of a hand trainer which eachhave identical dimensions and differ only in terms of the fiber contentof the plastic used for the spring elements. The spring elements wereproduced from polyoxymethylene (POM) with fiber contents of 0% byweight, 5% by weight, 10% by weight, 12.5% by weight, 15% by weight and20% by weight.

From the force-travel curves in FIG. 8, it will be seen that the handtrainers present a slightly non-linear behavior in the case of a shortdeformation travel, wherein the force needed for a defined deformationis increased with an increasing fiber content, in the hand trainers withspring elements made from the fiber-reinforced material. The handtrainer composed of the non-reinforced material has a more pronouncednon-linear characteristic, such that the force required for adeformation up to approximately 3 mm deformation is initiallyapproximately as high as in the case of the hand trainer with a fibercontent of 10% by weight. At a deformation travel of 10 mm, the forcerequired for the deformation of the hand trainer composed ofnon-reinforced material corresponds to that of the hand trainer with afiber content of 5% by weight. Above 10 mm, all hand trainers composedof materials reinforced with fibers have a greater required force thanthe hand trainer composed of the non-reinforced material. At the maximumtested deformation travel of 20 mm, the non-reinforced plastic has thelowest force, and the force needed fro a deformation of 20 mm increaseswith an increasing fiber content in the plastic.

LIST OF REFERENCE SIGNS

1 muscle trainer

2 length

4 width

5 width at the center

6 wall thickness of the end areas

7 wall thickness at the center

8 force introduction area

11 first spring element

12 second spring element

13 first end area

14 second end area

15 first joint element

16 second joint element

18 bracket

20 bearing

22 axis

24 roller

26 snap-in hook

28 projection

30 opening

32 long opening

34 wide opening

36 36 grip

38 spacer

40 distance, unloaded

42 distance, loaded

44 ram

46 table

48 deformation travel

F force application

1. A muscle trainer comprising a first curved, elongate spring elementand a second curved, elongate spring element, the two spring elementsbeing arranged with their concave sides facing each other, end areasbeing formed at each of the ends of the two spring elements, a firstjoint element being formed at a first end area of each spring elementand a second joint element being formed at a second end area of eachspring element, and the spring elements being connected to each other attheir two end areas via joints formed from the joint elements, whereinthe first joint elements are designed as brackets, the brackets having abend in the direction of the concave side of the respective springelement and in each case at least partially enclosing the second jointelement of the respective other spring element, the second jointelements, being designed as a roller or rounded, and the brackets eachforming a bearing in which the respective enclosed second joint elementis mounted rotatably.
 2. The muscle trainer according to claim 1,wherein the muscle trainer consists of precisely two spring elements. 3.The muscle trainer according to claim 1, wherein the first springelement and the second spring element have an identical geometry.
 4. Themuscle trainer according to claim 1, wherein a respective joint elementof the first spring element establishes a form-fit connection with ajoint element of the second spring element, which form-fit connectionprevents a lateral movement of the first spring element relative to thesecond spring element.
 5. The muscle trainer according to claim 4,wherein the form-fit connection is formed by in each case a snap-in hookon the second joint element, which snap-in hook in each case engages ina corresponding opening in the first end area of the respective otherspring element, the snap-in hook interacting with the opening toestablish a further form-fit connection which prevents a movement, inthe longitudinal direction, of the first spring element relative to thesecond spring element.
 6. The muscle trainer according to claim 5,wherein the snap-in hook has a projection which, by interaction with theopening in the first end area, establishes a form-fit connection whichprevents a vertical movement of the first spring element relative to thesecond spring element.
 7. The muscle trainer according to claim 1,wherein the first spring element and the second spring element are bothfree of undercuts.
 8. The muscle trainer according to claim 1, whereinthe two spring elements are produced from a thermoplastic, saidthermoplastic being chosen in particular from polyoxymethylene (POM),polybutylene terephthalate (PBT), polyamide (PA),acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP).
 9. Themuscle trainer according to claim 8, wherein the thermoplastic isfiber-reinforced.
 10. The muscle trainer according to claim 9, whereinan opposing force of the spring elements is adjustable through a choiceof a fiber content in the thermoplastic, the fiber content being chosenin a range from 1% by weight to 50% by weight.
 11. The muscle traineraccording to claim 1, wherein the spring elements each comprise a gripon a force introduction area.
 12. The muscle trainer according to claim11, wherein the grip is produced from a thermoplastic polyurethane(TPU).
 13. The muscle trainer according to claim 11, wherein the griphas, on the concave side of the spring element, a spacer for limitingthe bending.
 14. A method for producing a muscle trainer according toclaim 1, comprising the steps of: a) producing the first spring elementand the second spring element by injection molding using an injectionmold, b) arranging the first spring element and the second springelement such that their concave sides face each other and such that, atthe ends of the spring elements, a first joint element adjoins a secondjoint element of the respective other spring element, c) bending theends of the first spring element and of the second spring element byapplying a force to the spring elements, d) snapping a second jointelement into a respective first joint element, such that the first jointelements each at least partially enclose a second joint element of therespective other spring element, and e) terminating the forceapplication, wherein the joint elements of the spring elements formjoints.
 15. A method for training hand muscles comprising actuating amuscle trainer according to claim 1.